Surface interception and transport of ¹⁴C-labeled polystyrene nanoplastics by benthic marine organisms

The fate of nanoplastics (NPs) in marine environments may be strongly influenced by their interactions with benthic organisms, including surface retention and biological association. However, quantitative characterization of these processes remains challenging. In this study, ¹⁴C-labeled polystyrene NPs were synthesized to trace their interactions with the marine clam Ruditapes philippinarum and the fungus Schizophyllum commune, two benthic organisms with extensive particle-contact surfaces. In R. philippinarum, the gills acted as the primary filtration interface after 24 h of exposure, showing the highest ¹⁴C-equivalent NP burdens of 1.1 ± 0.3 and 8.8 ± 4.5 μg/g at exposure concentrations of 100 and 1000 μg/L, respectively. After 48 h, NP burdens decreased in the respiratory and digestive organs, while low ¹⁴C levels were detected in the heart (0.28 ± 0.17 μg/g at 100 μg/L), suggesting limited internal transfer. In S. commune, a minor fraction of ¹⁴C was strongly associated with mycelia after 42 d of liquid culture exposure at 1000 μg/L, but no measurable mineralization or depolymerization of NPs was observed. A plate-based solid-culture assay further showed hyphae-mediated distal transport of NPs, although particle internalization and translocation were not directly visualized. These findings indicate that benthic biological surfaces may serve as important reservoirs for NPs, influencing their persistence in marine benthic environments.